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Representative spectrograms of the songs produced by a same testosterone-treated male after 3, 10 and 24 days of exposure to the steroid. Panel A shows three very short songs (1–2 sec) produced after only 3 days of exposure to testosterone by a male who was not signing at all before. Panels B and C illustrate the fact that already after 10 days complex well-structured songs are produced by the castrated males treated with testosterone.
